[Qemu-devel] [PATCH v2 1/3] hw/vfio/platform: irqfd setup sequence update

[Eric Auger <eric.auger@linaro.org>]

With current implementation, eventfd VFIO signaling is first set up and
then irqfd is setup, if supported and allowed.

This start sequence causes several issues with IRQ forwarding setup
which, if supported, is transparently attempted on irqfd setup:
IRQ forwarding setup is likely to fail if the IRQ is detected as under
injection into the guest (active at irqchip level or VFIO masked).

This currently always happens because the current sequence explicitly
VFIO-masks the IRQ before setting irqfd.

Even if that masking were removed, we couldn't prevent the case where
the IRQ is under injection into the guest.

So the simpler solution is to remove this 2-step startup and directly
attempt irqfd setup. This is what this patch does.

Also in case the eventfd setup fails, there is no reason to go farther:
let's abort.

Signed-off-by: Eric Auger <eric.auger@linaro.org>
---
 hw/vfio/platform.c | 51 +++++++++++++++++++++++++++++----------------------
 1 file changed, 29 insertions(+), 22 deletions(-)

diff --git a/hw/vfio/platform.c b/hw/vfio/platform.c
index a6726cd..d864342 100644
--- a/hw/vfio/platform.c
+++ b/hw/vfio/platform.c
@@ -310,18 +310,29 @@ static void vfio_platform_eoi(VFIODevice *vbasedev)
 /**
  * vfio_start_eventfd_injection - starts the virtual IRQ injection using
  * user-side handled eventfds
- * @intp: the IRQ struct pointer
+ * @sbdev: the sysbus device handle
+ * @irq: the qemu irq handle
  */
 
-static int vfio_start_eventfd_injection(VFIOINTp *intp)
+static void vfio_start_eventfd_injection(SysBusDevice *sbdev, qemu_irq irq)
 {
     int ret;
+    VFIOPlatformDevice *vdev = VFIO_PLATFORM_DEVICE(sbdev);
+    VFIOINTp *intp;
+
+    QLIST_FOREACH(intp, &vdev->intp_list, next) {
+        if (intp->qemuirq == irq) {
+            break;
+        }
+    }
+    assert(intp);
 
     ret = vfio_set_trigger_eventfd(intp, vfio_intp_interrupt);
     if (ret) {
-        error_report("vfio: Error: Failed to pass IRQ fd to the driver: %m");
+        error_report("vfio: failed to start eventfd signaling for IRQ %d: %m",
+                     intp->pin);
+        abort();
     }
-    return ret;
 }
 
 /*
@@ -359,6 +370,15 @@ static int vfio_set_resample_eventfd(VFIOINTp *intp)
     return ret;
 }
 
+/**
+ * vfio_start_irqfd_injection - starts the virtual IRQ injection using
+ * irqfd
+ *
+ * @sbdev: the sysbus device handle
+ * @irq: the qemu irq handle
+ *
+ * In case the irqfd setup fails, we fallback to userspace handled eventfd
+ */
 static void vfio_start_irqfd_injection(SysBusDevice *sbdev, qemu_irq irq)
 {
     VFIOPlatformDevice *vdev = VFIO_PLATFORM_DEVICE(sbdev);
@@ -366,7 +386,7 @@ static void vfio_start_irqfd_injection(SysBusDevice *sbdev, qemu_irq irq)
 
     if (!kvm_irqfds_enabled() || !kvm_resamplefds_enabled() ||
         !vdev->irqfd_allowed) {
-        return;
+        goto fail_irqfd;
     }
 
     QLIST_FOREACH(intp, &vdev->intp_list, next) {
@@ -376,13 +396,6 @@ static void vfio_start_irqfd_injection(SysBusDevice *sbdev, qemu_irq irq)
     }
     assert(intp);
 
-    /* Get to a known interrupt state */
-    qemu_set_fd_handler(event_notifier_get_fd(&intp->interrupt),
-                        NULL, NULL, vdev);
-
-    vfio_mask_single_irqindex(&vdev->vbasedev, intp->pin);
-    qemu_set_irq(intp->qemuirq, 0);
-
     if (kvm_irqchip_add_irqfd_notifier(kvm_state, &intp->interrupt,
                                    &intp->unmask, irq) < 0) {
         goto fail_irqfd;
@@ -395,9 +408,6 @@ static void vfio_start_irqfd_injection(SysBusDevice *sbdev, qemu_irq irq)
         goto fail_vfio;
     }
 
-    /* Let's resume injection with irqfd setup */
-    vfio_unmask_single_irqindex(&vdev->vbasedev, intp->pin);
-
     intp->kvm_accel = true;
 
     trace_vfio_platform_start_irqfd_injection(intp->pin,
@@ -406,9 +416,11 @@ static void vfio_start_irqfd_injection(SysBusDevice *sbdev, qemu_irq irq)
     return;
 fail_vfio:
     kvm_irqchip_remove_irqfd_notifier(kvm_state, &intp->interrupt, irq);
+    error_report("vfio: failed to start eventfd signaling for IRQ %d: %m",
+                 intp->pin);
+    abort();
 fail_irqfd:
-    vfio_start_eventfd_injection(intp);
-    vfio_unmask_single_irqindex(&vdev->vbasedev, intp->pin);
+    vfio_start_eventfd_injection(sbdev, irq);
     return;
 }
 
@@ -646,7 +658,6 @@ static void vfio_platform_realize(DeviceState *dev, Error **errp)
     VFIOPlatformDevice *vdev = VFIO_PLATFORM_DEVICE(dev);
     SysBusDevice *sbdev = SYS_BUS_DEVICE(dev);
     VFIODevice *vbasedev = &vdev->vbasedev;
-    VFIOINTp *intp;
     int i, ret;
 
     vbasedev->type = VFIO_DEVICE_TYPE_PLATFORM;
@@ -665,10 +676,6 @@ static void vfio_platform_realize(DeviceState *dev, Error **errp)
         vfio_map_region(vdev, i);
         sysbus_init_mmio(sbdev, &vdev->regions[i]->mem);
     }
-
-    QLIST_FOREACH(intp, &vdev->intp_list, next) {
-        vfio_start_eventfd_injection(intp);
-    }
 }
 
 static const VMStateDescription vfio_platform_vmstate = {
-- 
1.8.3.2